Doped polysilicon is often employed as the gate material for complimentary metal-oxide-semiconductor (CMOS) devices because doped polysilicon enables the formation of dual work function devices needed for CMOS devices. For example, dual work function devices may be produced by doping the polysilicon gates differently depending on the specific device being formed. A dual work function is required because CMOS devices include both N channel transistors (NFETs) and P channel transistors (PFETs) which operate at different threshold voltages, and the threshold voltage of a transistor is directly related to the work function of the gate material, among other factors.
However, semiconductor technology is advancing towards replacing doped polysilicon gates with gates that substantially comprise metal. Hence, obtaining a dual work function configuration requires forming NFET gates that comprise one metal and PFET gates that comprise another metal.